Definition from Nolo’s Plain-English Law Dictionary
Alike in all relevant ways for purposes of a particular decision or issue. This term is often used in discrimination cases, in which the plaintiff may seek to show that he or she was treated differently from others who are similarly situated except for the alleged basis of discrimination. For example, a plaintiff who claims that she was not promoted because she is a woman would seek to show that similarly situated men -- that is, men with similar qualifications, experience, and tenure with the company -- were promoted. This term is also used to define the group of people on whose behalf a class action may be brought: Everyone in the group must be similarly situated as to the issue(s) litigated. For example, in a case alleging that a credit card company charged improper fees, only people who had a credit card with that company during the time when the improper fees were imposed could be members of the class.